Sound suppressor for reaction engines

ABSTRACT

1,075,028. Silencing gaseous streams. KOPPERS CO., Inc. Nov. 16, 1965 [Jan. 11, 1965], No. 48711/65. Heading F1B. A hollow pyramid structure is located in the gaseous stream with its apex pointing downstream. The pyramid includes a circular base 21 and five sides each comprising a main member 23 and branch members 27. Cooling water flows from inlet 28 through the hollow base 21, the hollow members 23 and 27 and finally into the gaseous stream through orifices 41 in the members 27. Each branch member 27 may be formed in two parts welded to the respective member 23 or, as shown, one part passing through member 23 and provided with an aperture 30 for coolant flow. A ground-based silencer for jet aircraft, Figs. 3 and 4 (not shown), comprises a pyramid structure supported by fins in a duct located downstream of and coaxial with the aircraft exhaust nozzle. The duct and a stack, into which the duct leads, may be double-walled with sound absorbing material between the walls. Air is drawn into the duct through lateral intakes adjacent the pyramid.

p 26, 1967 G. J. SANDERS 3,343,629

SOUND SUPPRESSOR FOR REACTION ENGINES I Filed Jan. 11, 1965 2 Sheets-Sheet 1 INVENTOR.

6U) J. .SANDEES Sept. 26, 1967 G. J. SANDERS SOUND SUPPRESSOR FOR REACTION ENGINES 2 Sheets-Sheet 2 Filed Jan. 11, 1965 FIG. 4

INVENTOR. 60) J SANDERS lZw/KW llis United States Patent Office 3,343,629 Patented Sept. 26, 1967 3,343,629 SOUND SUPPRESSOR FOR REACTION ENGINES Guy J. Sanders, Severna Park, Md., assignor to Koppers Company, Inc., a corporation of Delaware Filed Jan. 11, 1965, Ser. No. 424,679 3 Claims. (Cl. 181-52) ABSTRACT OF THE DISCLOSURE A sound suppressor for reaction engines, particularly jet engines, comprising a stack connected to the gas discharge portion of the engine and a noise attenuating diffuser within the stack adjacent the discharge portion, the diffuser comprising a frusto-conical, labyrinth structure having fiat unconnected sides with its base facing the exhaust gases, the diffuser preferably being cooled by water injected into the hollow structural members of the diffuser during after-burner operation.

This invention relates generally to apparatus for the diffusion of gas streams and more particularly to a diffuser for the suppression of exhaust noises from reaction engines.

Patent No. 3,165,167 illustrates a noise suppressor that is adapted to be placed adjacent to the exhaust of a reaction engine to intercept and redirect the hot gases. This patent shows the diffuser as comprising a series of concentric, circular hoops of successively decreasing diameters that are mounted on longitudinal support bars and thus arranged in a generally conical configuration. This diffuser promotes a rapid decrease in exhaust gas velocity and at the same timea rapid mixing of the gas with ambient air, but does not particularly affect engine temperature, thrust or performance since its efficient design offers a minimum pressure drop. I'iWhen the diffuser is designed for operation with ordinary jet engines where the exhaust temperatures are around 1100 F., the diffuser can be made of corrosionresistant carbon steel. Steel melts at about 1900 F. Rocket engines and jet engines that are equipped with an after-burner discharge gases at a higher temperature, for example, about 32003500 F. To use a diffuser at such high temperatures, the hoop-like members must be cooled as by flowing water through them to prevent their destruction.

When the hoop-like members are tubular and cooling water is flowed through them, the outer skin surface of the tube is subjected to a temperature of 3,000 F. or higher while the inner skin surface of the tube is subjected to a temperature of about 70 F the temperature of the cooling water. Such great thermal difference creates an intense stress relationship within the metal. Also the hooplike members must expand and contract as the temperatures rise and fall. As a result, it has been difficult to make welding hold at the joints and to keep the thermal expansion and contraction from fracturing the diffuser tubes.

This invention, therefore, provides a novel structure which minimizes or eliminates the structural stresses.

This invention contemplates a diffuser having a generally circular header that is adapted to receive the exhaust gases from the reaction engine, a plurality of trunks extend longitudinally from said header and radially inwardly to provide a structure of generally conical configuration, and branches extend laterally in a common axial plane from each trunk, the branches extending from each trunk being independent of the branches extending from the other trunks, but the branches of one trunk being directed toward the branches of the adjacent trunks.

Although this invention is useful for attenuating the exhaust gas noises of reaction engines, it is also useful in diffusing and attenuating noises of any high velocity gas stream, as for example, vented high pressure steam.

The above and further objects and novel features of the invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

In the drawings wherein like parts are marked alike:

FIGURE 1 is a side view with portions broken out of an embodiment of the novel diffuser of the present invention;

FIGURE 2 is an end view of the novel diffuser of FIG. 1;

FIGURE 3 is a side view of a sound suppressor associated with a jet aircraft and with portions broken away and the diffuser of FIG. 1 illustrated schematically;

FIGURE 4 is a top plan view of the suppressor of FIG. 3.

Referring to FIG. 4, the suppressor comprises generally an entrance 11, an augmenter'chamber 13, and a stack 15. As shown in FIG. 5, the entrance portion has air intakes 17 for the mixing of air with the exhaust gases. The velocity of the exhausts from the engine aspirates air into the unit. The augmenter and stack are usually double-walled and have acoustical packing material disposed between the walls.

In operation, the reaction engine illustrated here as being a portion of an aircraft 20 is placed adjacent the suppressor with the exhaust nozzle at the entrance portion 11. The exhaust gases from the engine are passed through the diffuser and mixed with ambient air, then passed into the augmenter or expansion chamber 13, and thence are passed through the stack 15. The foregoing, of course, is illustrated in Patent No. 3,165,167. Difficulties have been experienced, however, due to thermal stress resulting from the high temperature of the exhaust gases.

Referring now to FIG. 1, the embodiment of the novel diffuser illustrated there comprises generally circular header 21 that is adapted to receive the exhaust from the reaction engine. Extending longitudinally from and radially inwardly are a plurality of trunks 23. These trunks are secured at the end opposite from header 21 by a plate 25 which is preferably open at 26 to reduce air resistance. Header 21 and trunks 23 are hollow for the flow of water from inlet 28 through the header and trunks. The trunks are secured to header 21 and plate 25 by a conventional means as by welding.

Extending laterally from the trunks 23 are a plurality of branches 27. These branches are generally in an axial plane of the trunk and extend toward the branches of adjacent trunks. These branches 29 become smaller as the apex of the cone is reached at plate 25. The branches thus do not intersect but are independent of each other. The branches terminate in caps or solid heads 29 which are conveniently threaded on the branches. These branches are hollow and open into the trunks so that water can flow into the branches. Advantageously, the branches extend all the -Way through trunk 23 as illustrated in FIG. 1 and welded although obviously each branch such as 29L and 29R may be separate branches and may be welded individually to trunks 23. When a branch is an integral or one-piece unit, an aperture 30, of course, must be present inside the trunk to permit water to flow into the branch. The branches also have apertures 41 therethro'ugh which project water inwardly toward the apex of the cone. This water helps to cool the gas and at the same time provides for an interchange of water within the trunk and branches so that the water does not become heated but is continually flowing into and out from the branch and trunk.

The diffuser is maintained within the entrance by means of fins such as 31 which may be secured to the trunks of the ditfuser and also to the entrance Wall of the suppressor.

It has been found the novel diffuser of this invention with its individual branches does substantially the same amount of attenuation as did the integral rings of the aforementioned Patent No. 3,165,167. Since no rigid interconnection exists between the branches extending from one trunk and the branches extending from the other trunk, the free ends of the branches thus can accommodate to any thermal expansion and contraction without setting up great stresses.

said apex, said main members converging toward said longitudinal axis from said base to said apex;

a plurality of stub members spaced along each said main member and extending in a substantially flat plane from both sides thereof transversely to the flow of gases between said base and said apex,

said stub members being progressively shorter from said base to said apex and terminating short of transverse intersection with stub members extending from adjacent main members,

whereby said main members and said stub members form disconnected sides converging from said base to said apex of said pyramidal structure.

2. The noise attenuation apparatus of claim 1 wherein Typical of the performance of the novel diffuser of this said annular base portion, said main members, and said invention is the attenuation illustrated by the chart below:

stub members are hollow conduits and, in addition, means ACOUSIIOAL ANALYSIS Octave Bands Frequency (c.p.s.) -75 75-150 150-300 300-600 600-1, 200 1, 200-2, 400 2, 400-4, 800 4, 800-9, 600

Without Diffuser 94 94 88 88 84 78 71 64 With Diffuser 83 81 79 77 79 75 70 61 Attenuation in Decibles. 11 13 9 11 5 3 1 3 The foregoing represents attenuation in sound pressure level at a distance of 250 feet from a J-57 jet engine at full military power.

I claim:

1. Noise attenuation apparatus for gas streams comprising an entrance section adapted to receive said gases, a stack spaced downstream from said entrance section to discharge said gases and a diffuser between said entrance section and said stack extending longitudinally of the flow of gases for suppressing noise therein, said diffuser comprising:

a truncated pyramidal structure having a longitudinal axis substantially parallel to the flow of said gases; an annular base portion adjacent said entrance section through which said gases may flow;

an apex portion smaller than said base portion and spaced downstream therefrom along said longitudinal axis;

a plurality of main members connecting said base to are provided for flowing a cooling fluid into said hollow conduits.

3. The noise attenuation apparatus of claim 2 wherein said stub members have at least one aperture located substantially on the downstream side of said stub members for discharging said cooling fluid into the gas stream.

References Cited RICHARD B. WILKINSON, Primary Examiner.

R. S. WARD, Assistant Examiner. 

1. NOISE ATTENUATION APPARATUS FOR GAS STREAMS COMPRISING AN ENTRANCE SECTION ADAPTED TO RECEIVE SAID GASES, A STACK SPACED DOWNSTREAM FROM SAID ENTRANCE SECTION TO DISCHARGE SAID GASES AND A DIFFUSER BETWEEN SAID ENTRANCE SECTION AND SAID STACK EXTENDING LONGITUDINALLY OF THE FLOW OF GASES FOR SUPPRESSING NOISE THEREIN, SAID DIFFUSER COMPRISING: A TRUNCATED PYRAMIDAL STRUCTURE HAVING A LONGITUDINAL AXIS SUBSTANTIALLY PARALLEL TO THE FLOW OF SAID GASES; AN ANNULAR BASE PORTION ADJACENT SAID ENTRANCE SECTION THROUGH WHICH SAID GASES MAY FLOW; AN APEX PORTION SMALLER THAN SAID BASE PORTION AND SPACED DOWNSTREAM THEREFROM ALONG SAID LONGITUDINAL AXIS; A PLURALITY OF MAIN MEMBERS CONNECTING SAID BASE TO SAID APEX, SAID MAIN MEMBERS CONVERGING TOWARD SAID LONGITUDINAL AXIS FROM SAID BASE TO SAID APEX; A PLURALITY OF STUB MEMBRES SPACED ALONG EACH SAID MAIN MEMBER AND EXTENDING IN A SUBSTANTIALLY FLAT PLANE FROM BOTH SIDES THEREOF TRANSVERSELY TO THE FLOW OF GASES BETWEEN SAID BASE AND SAID APEX, SAID STUB MEMBERS BEING PROGRESSIVELY SHORTER FROM SAID BASE TO SAID APEX AND TERMINATING SHORT OF TRANSVERSE INTERSECTION WITH STUB MEMBERS EXTENDING FROM ADJACENT MAIN MEMBERS, WHEREBY SAID MAIN MEMBERS AND SAID STUB MEMBERS FORM DISCONNECTED SIDES CONVERGING FROM SAID BASE TO SAID APEX OF SAID PYRAMIDAL STRUCTURE. 